Waterborne zinc-rich primer compositions

ABSTRACT

A multi-component waterborne corrosion resistant coating composition used as an organic zinc rich primer for protecting metal substrate from corrosion. The composition includes zinc dust, a crosslinking component and a polymeric component produced from a low Tg polymer and an amine functional curing agent. These components of the composition are stored separately and then mixed prior to applying the coat of the composition over metal substrate. 
     The coating composition of the present invention has longer pot life than conventional waterborne corrosion resistant coating composition.

This is a divisional of application Ser. No. 08/407,514, filed on Mar.16,1995, now U.S. Pat. No. 5,569,6877.

The present invention generally relates powdered zinc-rich coatingcompositions suitable for use as anticorrosion protective coatings onmetal substrates and more particularly relates to waterborne zinc-richorganic primers suitable for protecting of steel substrates fromcorrosion.

Corrosion is the natural deterioration or destruction of a materialresulting from its interaction with the environment. The corrosionprocess is generally electrochemical it nature. The term is appliedmostly to metals and particularly to their reaction with oxygen andwater that results in corrosion of metallic surfaces. Several approacheshave been utilized in providing corrosion protection. One of the mostattractive approaches has been the use of zinc-rich coatings to preventcorrosion. Zinc is an active metal and it exhibits higher reducingpotential than many metals and their alloys, such as, for example, iron,cadmium, cobalt, nickel and copper metals and their alloys. Theamphoteric nature of zinc, forming divalent zinc ions in acid or neutralmedia and zincate ions in basic media, makes it useful as a reducingagent that protects less electronegative metals, such as, iron. Thus, aslong as physical contact is maintained, a coating of zinc will bepreferentially oxidized while the underlying metal substrate surface,which acts as an electrical conductor to transfer electrons from zinc tooxygen, is protected.

One of the means of protecting metal or metal alloy substrates, such assteel substrates, is to coat such surfaces with corrosion-resistantprimers, that incorporate powdered zinc, also known as zinc dust, as ametallic pigment. Zinc-rich primers are known in the art and have beencommercially available since the 1940s. Zinc-rich primers typicallyinclude film-forming organic or inorganic binders for binding the zincdust into a film. The present invention is directed to organicbinder-based zinc-rich primers. Organic binder-based zinc-rich primersemploy solvent borne or waterborne systems. Solvent borne primercompositions have a high volatile organic component (VOC), which makesthem undesirable due to environmental concerns and safety and healthissues. Therefore, zinc-rich primer manufacturers would like to reducethe organic solvent content through the use of substantially waterborneprimer coatings. For example, three-component waterborne coatings basedon a zinc-rich epoxy emulsion are described in Japanese patent Sho52-54724. One of the problems associated with such a waterbornecomposition is its short pot life. These compositions have a tendency toform a skin or crust in a very short time, i.e., in less than 1 to 2minutes, after the components are mixed to form a pot mix. The skin orcrust formation is undesirable since it not only results in coatings ofuneven thicknesses that provide poor rust protection but it also tendsto plug up orifices of nozzles of spray coating equipment typically usedin applying corrosion-resistant coating compositions. The presentinvention addresses the problem of short pot life by providing awaterborne multi-component zinc-rich primer having longer pot life thanthe known compositions. A pot mix of the claimed composition does notform a skin or crust, even over extended periods of 3 to 5 days andstill provides effective corrosion protection. As a result, thecomposition of present invention is capable of producing a corrosionprotective coating having uniform thickness.

Therefore, the present invention is directed to a multi-componentcorrosion-resistant waterborne coating composition comprising:

a polymeric component comprising an aqueous dispersion of polymerparticles of a latex polymer having a Tg in the range of -50° C. to +50°C. and a stabilizing amount of an amine-functional curing agent;

a crosslinking component coreactable with the amine-functional curingagent; and

a corrosion protector component comprising a corrosion resisting amountof a zinc dust, wherein the stabilizing amount of the amine-functionalcuring agent is sufficient to stabilize the polymer particles in theaqueous dispersion in the presence of the corrosion protector component.

The present invention is further directed to a method of producing acorrosion-resistant coating on a metal substrate comprising:

mixing a stabilizing amount of an amine-functional curing agent withpolymer particles of a latex polymer having a Tg in the range of -50° C.to +50° C. to form an aqueous dispersion of a polymeric component;

mixing a corrosion protector component comprising a corrosion resistingamount of a zinc dust with the polymeric component whereby the aqueousdispersion of the polymer particles is stabilized in the presence of thecorrosion protector component by the amine-functional curing agent;

mixing a crosslinking component coreactable with the amine-functionalcuring agent with the mixture of the polymeric and the corrosionprotector components to a form a pot mix;

applying a layer of the pot mix on the metal substrate; and

crosslinking the amine-functional curing agent with the crosslinkingcomponent in the layer to form the corrosion-resistant coating on themetal substrate.

The inventive aspect of the present invention is the dual role played bythe amine-functional curing agent in the waterborne zinc-richcomposition.

Firstly, the applicants have discovered that by incorporating astabilizing amount of the amine-functional curing agent in thecomposition, which contains an aqueous dispersion of latex polymerparticles and zinc dust, the dispersion stability of such latex polymerparticles is maintained by the curing agent in the presence of the zincdust in the composition. It is believed, without reliance thereon, thatthe reactive amine of the curing agent associates with the latex polymerparticles and thereby prevents zinc from gelling the polymer particlesand thus preventing the rapid skin or crust formation.

Secondly, the applicants have discovered that once a coating of thepresent composition is applied over a metal surface, the aminefunctional curing agent, which helps stabilize the latex polymer duringthe initial stage, then crosslinks with a crosslinking component of thecomposition and thereby substantially eliminates the amine functionalityfrom the coating of the present composition. The removal of the aminefunctionality from the coating of the composition is important since itspresence leads to a water sensitive coating having poor rust protection.

As used herein:

"Latex polymer" means latex polymer particles dispersed in an aqueousmedium.

"Emulsion polymer" is a latex polymer produced by the emulsionpolymerization process.

"Polymeric component" is a film forming substance or a combination ofsubstances which includes a latex polymer, coalescing agents,surfactants and an evaporable carrier phase, such as water. Thepolymeric component may optionally include a pigment.

"Composition solids" means weight of the composition in its dry state.

"Waterborne coating composition" means a composition that utilizes wateras the primary continuous dispersing phase.

"Solvent borne coating composition" means a composition that utilizes anorganic solvent as the primary continuous dispersing phase.

"Multi-component (also known as multi-package) composition" means acomposition having two or more components that are stored separately andthen mixed to form a pot mix, which is then applied as a coating on ametal surface.

"Pot life" means a period of time beyond which a pot mix develops skinor crust and is too viscous to be applied effectively as a coating on asubstrate.

The multi-component corrosion-resistant waterborne coating compositionof the present invention generally includes from 5 percent to 30percent, preferably from 10 percent to 18 percent, by weight of thecomposition solids of a polymeric component. The polymeric componentincludes an aqueous dispersion of polymer particles of a latex polymer,preferably a hydrophobic latex polymer. The polymeric componentgenerally includes from 5 percent to 15 percent, preferably 8 percent to12 percent, by weight of the composition solids of the latex polymer.

The latex polymer of the present invention may be copolymerized from atleast one comonomer, such as, for example, an alpha, beta-ethylenicallyunsaturated monomer, including styrene, butadiene, alpha-methylstyrene,vinyl toluene, vinyl naphthalene, ethylene, vinyl acetate, vinylversatate, vinyl chloride, vinylidene chloride, acrylonitrile,methacrylonitrile, (meth)acrylamide; various (C1-C20) alkenyl esters of(meth)acrylic acid, such as, for example, methyl (meth)acrylate, ethyl(meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate,2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, n-octyl(meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate,tetradecyl (meth)acrylate, n-amyl (meth)acrylate, neopentyl(meth)acrylate, cyclopentyl (meth)acrylate, lauryl (meth)acrylate,oleyl(meth)acrylate, palmityl (meth)acrylate, and stearyl(meth)acrylate; other (meth)acrylates, such as, isobornyl(meth)acrylate, benzyl (meth)acrylate, phenyl (meth)acrylate.2-bromoethyl (meth)acrylate, 2-phenylethyl (meth)acrylate, and1-naphthyl (meth)acrylate; alkoxy-alkyl (meth)acrylate, such as,ethoxyethyl (meth)acrylate; mono- and dialkyl esters of ethylenicallyunsaturated di- and tricarboxylic acids and anhydrides, such as, ethylmaleate, dimethyl fumarate, trimethyl aconitate, and ethyl methylitaconate. As used herein, "(meth)acrylate" denotes both "acrylate" and"methacrylate."

The ethylenically unsaturated monomer may also include in the range offrom 0 to 5 percent by weight based on the total weight of compositionsolids, of at least one multi-ethylenically unsaturated monomereffective to raise the molecular weight and to crosslink the polymer.Examples of multi-ethylenically unsaturated monomers that can be usedinclude allyl (meth)acrylate, tripropyleneglycol di(meth)acrylate,diethyleneglycol, di(meth)acrylate, ethyleneglycol di(methyl)acrylate,1,6-hexanediol di(meth)acrylate, 1,4-butylene glycol dimethacrylate,1,3-butyleneglycol (meth)acrylate, polyalkylene glycol,di(meth)acrylate, diallyl phthalate, trimethylolpropane,tri(meth)acrylate, divinyl benzene, divinyl toluene, trivinyl benzeneand divinyl naphthalene.

The latex polymer of the present invention is preferably polymerizedfrom a monomeric mixture that includes amounts in the range of from 0 to10 percent, preferably in the range of from 0.1 to 4 percent, all basedon the total weight of the composition solids, of a stabilizingcopolymerizable monomer, which improves the dispersion stability of theparticles of the latex polymer. Examples of stabilizing copolymerizablemonomers include acrylamide, methacrylamide, acrylic acid, methacrylicacid, itaconic acid and beta-acryloxypropionic acid.

Copolymerizable monomers having other types of functionality, such as,adhesion-promoting monomers disclosed in U.S. Pat. No. 2,871,223 toHarkins et al., in the range of from 0.1 to 2 weight percent, based onthe total weight of the composition solids, may also be included thelatex polymer of the present invention. The method for preparing suchadhesion monomers is disclosed in U.S. Pat. No. 5,071,902 to Langerbeinset al.

More preferably the latex polymer is copolymerized from a monomericmixture containing 20 to 55 weight percent of alkyl acrylate, such as,butyl acrylate or 2-ethylhexylacrylate, 40 to 80 weight percent ofstyrene or alkyl methacrylate, such as, methyl methacrylate or butylmethacrylate, and 0 to 5 weight percent of methacrylic acid, acrylamide,acrylic acid or mixtures thereof. All these weight percentages are basedon the total weight of the composition solids.

The glass transition temperature of the latex polymer is in the range offrom -50° C. to +50° C., preferably from +10° C. to +16° C., as measuredby differential scanning calorimetry (DSC). To measure the Tg by thismethod, the copolymer samples were dried, preheated to 120° C., rapidlycooled to -100° C., and then heated to 150° C. at a rate of 20°C./minute while data was being collected. The Tg was measured at themidpoint of the inflection using the half-height method.

The polymerization techniques used tot prepare the latex polymer arewell known in the art. The latex polymer may be prepared by aqueoussolution polymerization with subsequent dispersion or by emulsionpolymerization. Emulsion polymerization is preferred. Either thermal orredox initiation processes may be used.

The polymerization process is typically initiated by conventional freeradical initiators, such as, for example, hydrogen peroxide, benzoylperoxide, t-butyl hydroperoxide, t-butyl peroctoate, ammonium and alkalipersulfates, typically at a level of 0.05 percent to 3.0 percent byweight, all weight percentages based on the weight of total monomer.Redox systems using the same initiators coupled with a suitablereductant such as, for example, isoascorbic acid and sodium bisulfitemay be used at similar levels.

Chain transfer agents, such as, for example, mercaptans may be used inan amount effective to provide a GPC weight average molecular weight of25,000 to 1,000,000. "GPC weight average molecular weight" means theweight average molecular weight determined by gel permeationchromatography (GPC) described on page 4, Chapter I of TheCharacterization of Polymers published by Rohm and Haas Company,Philadelphia, Pa. in 1976, utilizing polymethyl methacrylate as thestandard.

The diameter of the latex polymer is typically controlled by the amountof conventional surfactants added during the emulsion polymerizationprocess. Conventional surfactants include anionic, nonionic emulsifiersor their combination. Typical anionic emulsifiers include alkali orammonium alkyl sulfates, alkyl sulfonic acids, alkyl phosphonic acids,fatty acids, and oxyethylated alkyl phenol sulfates and phosphates.Typical nonionic emulsifiers include alkylphenol ethoxylates,polyoxyethylenated alkyl alcohols, amine polyglycol condensates,modified polyethoxy adducts, polyoxyethylenated mercaptans, long chaincarboxylic acid esters, modified terminated alkylaryl ether, andalkylpolyether alcohols. Preferred diameter of the polymer is in therange from 50 to 600 nanometers, and more preferably in the range from80 to 200 nanometers.

Alternatively, the latex polymer may include multi-stage polymerparticles having to or more phases of various geometric structures, suchas, for example, core/shell or core/sheath particles, core/shellparticles with shell phases incompletely encapsulating the core,core/shell particles with a multiplicity of cores and interpenetratingnetwork particles. In all of these cases the majority of the surfacearea of the particle will be occupied by at least one outer phase andthe interior of the latex polymer particle will be occupied by at leastone inner phase. The outer phase of the multi-stage polymer particlesweighs 5 weight percent to 95 weight percent based on the total weightof the particle. A GPC weight average molecular weight of thesemulti-stage polymer particles is preferably in the range of 5000 to2,000,000.

The multi-stage polymer particles are prepared by conventional emulsionpolymerization process in which at least two stages differing incomposition are formed in a sequential fashion. Such a process usuallyresults in the formation of at least two polymer compositions. Each ofthe stages of the multi-stage polymer particles may contain the samemonomers, chain transfer agents, surfactants, as those disclosed earlierfor the polymer particles. The emulsion polymerization techniques usedfor preparing such multi-stage polymer particles are well known in theart and are disclosed, for example, in the U.S. Pat. Nos. 4,325,856,4,654,397 and 4,814,373.

The polymeric component of the present invention further includes astabilizing amount of an amine-functional curing agent. The stabilizingamount means the amount of the amine-functional curing agent required toensure dispersion stability of the polymer particles in the presence ofzinc dust. Thus, higher the amount of zinc dust present in thecomposition, more will be the amount of the curing agent required toensure dispersion stability of the polymer particles and vice versa. Thestabilizing amount of the amine-functional curing agent in thecomposition is generally adjusted to be in the range of from 0.1 to 6weight percent, preferably in the range of from 0.5 to 3 weight percent,all based on the total weight of the composition solids.

Any non-polymeric polyfunctional amine having at least 2 primary orsecondary amino groups can be employed as the amine-functional curingagent in the present invention. Such amines include aliphatic andcycloaliphatic amines each having 2 to 10 primary or secondary aminogroups and 2 to 100 carbon atoms. Preferred non-polymeric polyfunctionalamines include 2 to 4 primary amino groups and 2 to 20 carbon atoms.Still further in this regard, suitable non-polymeric polyfunctionalamines include, but not limited hexamethylene diamine; 2-methylpentamethylene diamine; 1,3-diamino propane; 1,3-diamino pentane;dodecane diamine; 1,2-diamino cyclohexane; 1,4-diamino cyclohexane;para-phenylene diamine; 3-methyl piperidine; piperazine; N-aminoethylpiperazine; isophorone diamine; bis-hexamethylene triamine;diethylene triamine; ethylene diamine; diethylamine triamine;triethylene tetramine; tris(2-aminoethyl) amine; ethylene oxide-amine;polyoxyalkylene amines, such as, Jeffamine® D, ED and T seriespolyoxypropylene amine, supplied by Texaco Chemical Company of Houston,Tex.; amine-functional acrylic resins, disclosed in U.S. Pat. No.4,120,839; trimethyl hexamethylene diamine; and tetraethylene pentamine.Mixtures of these amine-functional curing agents can also be used. Themost preferred epoxy curing agent is a polyoxypropylene amine having theformula: ##STR1## which is supplied under the trademark Jeffamine ®D-230 polyoxypropylene amine; by Texaco Chemical Company, Houston Tex.

The polymeric component of the present invention optionally includes acorrosion inhibiting pigment for enhancing the corrosion protectionprovided by the resulting composition. The polymeric component includesin the range of from 0 to 15 percent, preferably in the range of from 1to 5 percent, all by weight percent based on the composition solids, ofthe corrosion inhibiting pigment. The suitable particle size of thecorrosion inhibiting pigment is in the range of 5 to 50, preferably inthe range of 10 to 20 micrometers.

Some of the corrosion inhibiting pigments suitable for use in thepresent invention include zinc oxide; modified barium metaborate soldunder the trademark Busan® 11M1 barium metaborate and supplied byBuckman Laboratories, Memphis, Tenn.; zinc hydroxy phosphite sold underthe trademark Nalzin® 2 supplied by NL Industries, Heightstown, N. J.,aluminum tripolyphosphate modified by zinc ion and silicate sold underthe trademark K-white® 84 supplied by Tayca Corp., Tokyo, Japan; Zincphosphate; basic zinc molybdenum phosphate; strontium chromate andstrontium zinc phosphosilicate. The preferred the corrosion inhibitingpigment is a basic zinc molybdenum phosphate sold under the trademarkHeucophos® ZMP supplied by Heucotech Limited, Fairless Hills, Pa.

The pot life of the present composition is in the range of from 3 to 5days. By contrast, zinc-rich compositions known in the art have a potlife of an hour to up to 8 hours.

Depending on the intended use of the composition, additional componentsmay be added to the polymeric component. These additional componentsinclude but not limited to defoamers, waxes, silicone-based slipadditives, wetting agents, preservatives, plasticizers, thickeners,dispersants, cosolvents and freeze/thaw protectors.

The composition of the present invention includes a crosslinkingcomponent, stored separately from the polymeric component until the useris ready for coating application. The number equivalent amount ofcrosslinking component of the present composition is stoichiometricallyselected based on the number equivalent amount of the amine-functionalcuring agent present in the polymeric component. The stoichiometricratio of the crosslinking component to the amine-functional curing agentvaries in range of from 0.5 to 2, preferably in the range of from 0.8 to1.2. Most preferably the stoichiometric ratio is 1. Preferably, thecrosslinking component is in a liquid state at the applicationtemperature, i.e., the temperature at which the coating composition isapplied to a substrate. Such a temperature is preferably the ambienttemperature. The crosslinking component may be emulsified in water ordissolved in water with a cosolvent, such as, ethylene glycol monobutylether. The crosslinking component in an emulsified form is preferred.Some of the suitable crosslinking components include reaction productsof epichlorohydrin with bisphenol A or bisphenol F containing at leasttwo oxirane rings; epoxidized novolac resins formed by reaction ofepichlorohydrin with the reaction product of phenol with formaldehyde;reaction products of epichlorohydrin and an aliphatic polyol, such as,glycerol. An aqueous emulsion of the reaction product of epichlorohydrinwith bisphenol A, such as, the one from Shell Chemical Co. known asEpi-Rez ® CMD W 60-3510 emulsified epoxy resin is more preferred. Theapplicants contemplate the crosslinking component to include an epoxyfunctionality having more than one epoxy group.

The composition of the present invention includes a corrosion resistingamount of a corrosion protector component that includes zinc dust. Thecorrosion protector component is preferably stored separately from thepolymeric component and the crosslinking component until the user isready for a coating application. The corrosion resisting amount of thezinc dust used in the present composition is in the range of from 60 to93 weight percent, preferably in the range of from 75 to 85 weightpercent, all based on the weight of the composition solids.

The important aspect of the zinc dust is its particle size. The zincdust having higher percentage of particles with smaller particle size,provides more surface area, which increases the physical contact betweenthe zinc dust and the underlying metal surface being protected. Asstated earlier, such increased contact results in improved corrosionprotection. The particle size of the zinc dust is commercially availablein "Standard size", "Fine size" and "Very fine size". The zinc dustparticles having "Very fine size" are preferred. Table 1 below providesthe desired particle size distribution:

                  TABLE 1    ______________________________________              Standard Size                        Fine Size                                 Very Fine Size    ______________________________________    Weight median                8           5        4    diameter, μm*    Percentage smaller                65          95       99    than 10 μm* diameter    Surface area, square                0.1         0.16     0.2    meter/gram    Apparent density,                3040        2400     2240    kilogram/meter cube    Particles under 44 μm*                98          99       100    ______________________________________     *μm is micrometers.

The more preferred zinc dust meets the specification D-520-51(recertified in 1976) established by American Society for TestingMaterials, Philadelphia, Pa. and shown in Table 2 below:

                  TABLE 2    ______________________________________                    Type 1*                          Type 2*    ______________________________________    Total zinc (minimum)                      97.5    98.0    Metallic zinc (minimum)                      94.0    94.0    Materials other than                      1.5     N.A.    metallic zinc and zinc    oxide    CaO (maximum)     0.7     0.7    Pb (maximum)      N.A.    0.01    Fe (maximum)      N.A.    0.02    Cd (maximum)      N.A.    0.02    Cl (maximum)      N.A.    0.01    S as SO.sub.3 (maximum)                      N.A.    0.01    Moisture (maximum)                      0.1     0.1    Oils (maximum)    N.A.    0.05    Zinc oxide residue                      6.0     Remainder    Dust particle size +150                      None    0.1    μm**    Dust particle size +75                      N.A.    0.8    μm**    ______________________________________     *All in weight percentages, N.A. means not available, and     **μm is micrometers.

The specification for Type II zinc dust in Table 2 was developed forapplications, such as, coated water pipes carrying potable water orcoated metal containers used for storing food. Of particular concern insuch applications are the contents of lead and cadmium, with respectivemaxima at 0.01 percent and 0.02 percent based on the total weight of thezinc dust.

The most preferred zinc dust suitable for use in the invention is ZincDust 64 supplied by Zinc Corporation of America, Monaca, Pa.

The corrosion protector component optionally includes zinc oxide, talcand silica dust.

The corrosion protector component further optionally includes copperdust. The presence of copper dust is especially suitable foranti-fouling paints used in the marine environments, such as, ship hullsand bottoms. It is believed without reliance thereon, that the presenceof copper dust in the composition of the present invention isparticularly inimical to the marine organisms responsible for barnaclegrowth and other fouling organisms.

Another embodiment of the present invention is a two-componentcorrosion-resistant waterborne composition that includes the polymericcomponent and a solvent dispersion of the cross linking component inwater miscible solvent, such as, ethylene glycol monobutyl ether, andthe corrosion protector component mixed therein.

To produce a corrosion-resistant coating on metal substrates, such steelsubstrates, the polymeric component of the present invention is mixedwith the corrosion protector component and the crosslinking component toa form a pot mix. The pot life of the pot mix is in the range of from 3to 5 days. The pot mix is prepared and then applied over the substratepreferably within 16 to 24 hours by conventional means, such spraying orbrushing.

It is contemplated that coatings produced from rite composition of thepresent invention may be used as a primer coat of a corrosion protectionsystem. The corrosion protection system typically includes a primer coathaving a thickness in the range of from 25 micrometers to 125micrometers, preferably 75 micrometers, applied over a metallicsubstrate and a top coat having a thickness in the range of from 25micrometers to 125 micrometers, preferably 75 micrometers, applied overthe primer coat. Optionally a mid-coat having a thickness in the rangeof from 25 micrometers to 125 micrometers, preferably 75 micrometers,may be applied between the primer coat and the top coat. The top coatand the mid-coat, if present, are typically produced from suitablepolymers, such as, latex polymers, which are preferably pigmented.

The present composition is suitable for use in many primer applications,such as, for example, coatings on appliances, nuclear power plants,coiled metal, maintenance coatings, off-shore drilling rigs, oil supertankers, pilings, oil and water pipelines, ship super structures, shopcoats, stacks, storage tanks, transmission towers, metal bridges andoutdoor steel structures; railroad cars; ship hulls and other marinestructures, such as, piers. The present composition is also suitable forOEM automotive applications, such as, for example protecting theautomotive underbodies front corrosion by the inorganic salts used toaid removal of ice and snow from highways and city streets. Theautomotive underbodies or doors or other restrictive areas of theautomobile may be dip coated, spray coated or injected with the coatingof the present invention to protect the underlying metal substrates fromcorrosion.

The following test procedures were used for generating the data reportedin the Examples below:

1) Dispersion instability of the polymer particles in an unstirred potmix was determined visually by the presence or absence of a skin orcrust in the pot mix. Absence of skin or crust formation indicatesdispersion stability.

2) Salt spray exposure test performed under ASTM B117-90 established byAmerican Society of Testing Materials, Philadelphia, Pa., exposes acoated metal plate specimen to a continuous salt spray of a 5% sodiumchloride solution at 95° F.

3) Humidity exposure test conducted under the same procedure as above,except the salt spray was replaced with a deionized (DI) water spray.

In all these exposure tests, the coated specimens were exposed for atleast 96 hours to determine the extent of corrosion of the underlyingmetal substrate and blistering of the corrosion resistant coatingthereon. The coating was considered to have passed these exposure testsif less than 10 percent area of the underlying metal substrate exhibitsrust and if less than 10 percent area of the corrosion resistant coatingdevelops blisters. The readings for rust formation were expressed interms of the percentage of the coated area exhibiting rust, i.e., norust would have a reading of 0 and totally rusted surface would have areading of 100. Similarly, the readings for blister formation wereexpressed in terms of the percentage of the coated area with blisters,i.e., a coated surface with no blisters would have a reading of 0 and atotally blistered surface would have a reading of 100.

The metal plate specimens used for these exposure tests were 10.2cms×10.2 cms cold rolled rectangular steel plates having a thickness of0.0635 millimeters (2.5 mil). Prior to coating, these specimens werecleaned by air grit blasting to remove any dirt, grease and rust spots.

Unless stated otherwise, all percentages and proportions given in thefollowing examples or in the test procedures described above are byweight based on the total weight of the composition.

The Examples 1, 2 and 3, shown in Table 3 below, were prepared andtested to establish the stabilizing role played by the amine-functionalcuring agent in maintaining the stability of the aqueous dispersion ofthe present composition in the presence of zinc dust and also todetermine the effect of the hydrophobicity of the latex polymer used inthe composition on the corrosion resistance of the resultingcomposition.

                  TABLE 3    ______________________________________            Example 1 Example 2  Example 3    ______________________________________    Polymeric    component    Water     10.17       10.17      10.36    Flash Rust              1.30        1.30       1.32    Preventive.sup.1    Dispersant.sup.2              0.28        0.28       0.29    Thickener.sup.3              0.10        0.10       0.10    Defoamer.sup.4              0.09        0.09       0.09    Latex Polymer              15.54*      12.67*     12.67*              46.5 BA/53.2                          46.5 BA/53.2                                     48 BA/46.5 Sty/3              MMA/1.3     MMA/1.3    AM/2.5 AA              MAA         MAA    Amine-functional              0.0         1.29       1.29    curing agent.sup.5    Corrosion 67.82       69.09      69.09    protector    component.sup.6    Epoxy resin              4.69        4.69       4.77    component.sup.7    ______________________________________     Abbreviated monomers are BA = Butyl Acrylate, MMA = methyl methacrylate,     AA = Acrylic acid, AM = acrylamide, MAA = methacrylic acid and Sty =     styrene.     *latex Polymer is an aqueous dispersion of 50 percent by weight.     **latex Polymer is an aqueous dispersion of 45 percent by weight.     Unless stated otherwise the following components were used in the above     Examples:     1 = an aqueous solution of 15 percent by weight sodium nitrite is supplie     by Baker Chemicals.     2 = Tamol ® 165 Dispersant is an aqueous solution of 22 percent by     weight supplied by Rohm and Haas Company, Philadelphia, Pennsylvania.     3 = Acrysol ® QR708 Thickener is an aqueous solution of 35 percent by     weight supplied by Rohm and Haas Company, Philadelphia, Pennsylvania.     4 = Tego Foamex ® 825 defoamer is an aqueous solution of 25 percent b     weight supplied by TegoChemie, USA, Hope Well, Virginia     5 = Jeffamine ® D230 is supplied by Texaco Chemical Company, Houston,     Texas     6 = Zinc Dust No. 64 is supplied by Zinc Corporation of America, Monaca,     Pennsylvania     7 = EpiRez ® CMD W 603510 epoxy resin is an aqueous solution of 65     percent by weight supplied by Shell Chemical Co., Houston, Texas

The polymeric component of Example 1 was prepared by mixing the variousingredient in the order shown in Table 3. The corrosion protectorcomponent was then mixed with the polymeric component and after 10minutes of mixing, an emulsified crosslinking component was added. InExample 1, skin and crust formation took place, within 2 minutes afterthe stirring was stopped.

The polymeric component of Examples 2 and 3 was prepared by premixingthe amine-functional curing agent with the latex polymer and thenallowing the mixture to stand for 24 hours. Various ingredients of thepolymeric component listed in Table 3 were then added in the ordershown. The corrosion protector component was then mixed with thepolymeric component and after 10 minutes of mixing an emulsifiedcrosslinking component was added. No skin or crust formation wasobserved and the compositions of Examples 2 and 3 did not destabilizeeven after five days at ambient conditions (24° C. at 50% relativehumidity). Thus, it is seen that the presence of the amine-functionalcuring agent in the compositions of Examples 2 and 3 preventsdestabilization of the aqueous dispersion of the latex polymer in thepolymeric component of the present coating composition.

Example 3 was compared with Example 2 to determine the effect of thehydrophobicity of the latex polymer utilized in the polymeric componentsof Examples 2 and 3 on the degree of corrosion protection provided bythe coating of the resulting compositions. The metal plate specimenswere coated within two hours after preparing the compositions ofExamples 2 and 3 and then tested for rust and blister formation underthe salt spray and humidity exposure tests. One set of coated specimenswere force dried in a recirculating air oven at a temperature of 60° C.for 30 minutes (Force dry). After 24 hours under ambient conditions, theforce dried specimens were exposure tested for 750 hours. Another set ofcoated specimens were air dried under ambient conditions for a week (Airdry) and then exposure tested for 500 hours. Results are tabulated inTables 4 and 5 below:

                  TABLE 4    ______________________________________    Rust Ratings                     Example 2                            Example 3    ______________________________________    Salt Spray  Force Dry  5        5                Air dry    10       0    Humidity    Force dry  0        0                Air dry    0        0    ______________________________________

                  TABLE 5    ______________________________________    Blister Ratings                     Example 2                            Example 3    ______________________________________    Salt Spray  Force Dry  0        0                Air dry    40       20    Humidity    Force dry  50       20                Air dry    80       40    ______________________________________

By analyzing Tables 4 and 5, it is seen that Example 3 which includes amore hydrophobic latex polymer, i.e., a latex polymer prepared from astyrene monomer, provides better ruse and blister protection thanExample 2.

Examples 4, 5 and 6, described below in Table 6, having differentamine-functional curing agents were prepared by using the proceduredescribed in Example 2.

                  TABLE 6    ______________________________________               Example 4 Example 5                                  Example 6    ______________________________________    Polymeric    component    Water        10.36       10.28    10.31    Flash Rust   1.32        1.32     1.32    Preventive.sup.1    Dispersant.sup.2                 0.29        0.29     0.29    Thickener.sup.3                 0.10        0.10     0.10    Defoamer.sup.4                 0.09        0.09     0.09    Latex Polymer                 12.67#      12.57#   12.61#    46.5 BA/53.2 MMA/1.3    MAA    Amine-functional                 1.29*       2.05*    1.74***    curing agent.sup.5    Corrosion    69.09       68.52    68.79    protector    component.sup.6    Epoxy resin  4.78        4.74     4.76    component.sup.7    ______________________________________     Abbreviated monomers are BA = Butyl Acrylate, MMA = methyl methacrylate,     MAA = methacrylic acid, Sty = styrene.     #latex Polymer is an aqueous dispersion of 50 percent by weight.     Unless stated otherwise the following components were used in the above     Examples:     1 = an aqueous solution of 15 percent by weight sodium nitrite is supplie     by Baker Chemicals.     2 = Tamol ® 165 Dispersant is an aqueous solution of 22 percent by     weight supplied by Rohm and Haas Company, Philadelphia, Pennsylvania.     3 = Acrysol ® QR708 Thickener is an aqueous solution of 35 percent by     weight supplied by Rohm and Haas Company, Philadelphia, Pennsylvania.     4 = Tego Foamex ® 825 defoamer is an aqueous solution of 25 percent b     weight supplied by TegoChemie, USA, Hope Well, Virginia     5 = Jeffamine ® D230 is supplied by Texaco Chemical Company, Houston,     Texas     * = Jeffamine ® D230 curing agent, ** = Jeffamine ® D400 curing     agent and *** = Jeffamine ® T403 curing agent     6 = Zinc Dust No. 64 is supplied by Zinc Corporation of America, Monaca,     Pennsylvania     7 = EpiRez ® CMD W 603510 epoxy resin is an aqueous solution of 65     percent by weight supplied by Shell Chemical Co., Houston, Texas

Metal plate specimens were coated with the compositions of Examples 4, 5and 6 and then force dried by the procedure described earlier. Thespecimens were then exposure tested for 750 hours to determine whichamine-functional curing agent provides better corrosion protection. Thetest results are listed in Table 7 below,

                  TABLE 7    ______________________________________    Rust Ratings                Example 4                         Example 5                                  Example 6    ______________________________________    Salt Spray             Force Dry                      10         90     30    Humidity Force dry                      0          5      5    ______________________________________

From Table 7, it is seen that Example 4, which includes Jeffamine® D-230curing agent, provides better protection than the other twoamine-functional curing agents.

Finally, Examples 7 and 8, described in Table 8 below, were prepared toobserve the effect of the inclusion of a corrosion inhibiting pigment onthe enhancement of corrosion protection provided by the composition ofthe present invention.

                  TABLE 8    ______________________________________                     Example 7                            Example 8    ______________________________________    Polymeric component    Water              1.4      1.3    Flash Rust Preventive.sup.1                       1.15     1.06    Latex Polymer      17.29*   16.00*    46.5 BA/53.2 MMA/1.3 MAA    Water              6.80     2.21    Dispersant.sup.2   0.24     0.22    Thickener.sup.3    0.25     0.23    Defoamer.sup.4     0.08     0.07    Amine-functional curing agent.sup.5    Corrosion inhibiting Pigment.sup.6                       0        7.48    Corrosion protector                       68.07    62.96    component.sup.7    Epoxy resin component.sup.8                       4.71     4.36    ______________________________________     Abbreviated monomers are BA = Butyl Acrylate, MMA = methyl methacrylate,     MAA = methacrylic acid, Sty = styrene.     *latex Polymer is an aqueous dispersion of 50 percent by weight.     Unless stated otherwise the following components were used in the above     Examples:     1 = an aqueous solution of 15 percent by weight sodium nitrite is supplie     by Baker Chemicals.     2 = Tamol ® 165 Dispersant is an aqueous solution of 22 percent by     weight supplied by Rohm and Haas Company, Philadelphia, Pennsylvania.     3 = Acrysol ® SCT270 Thickener is an aqueous solution of 21 percent b     weight supplied by Rohm and Haas Company, Philadelphia, Pennsylvania.     4 = Tego Foamex ® 825 defoamer is an aqueous solution of 25 percent b     weight supplied by TegoChemie, USA, Hope Well, Virginia     5 = Jeffamine ® D230 is supplied by Texaco Chemical Company, Houston,     Texas     6 = Heucophos ® ZMP zinc molybdenum phosphate is supplied by ZMP Co.,     Fairless Hills, Pennsylvania     7 = Zinc Dust No. 64 is supplied by Zinc Corporation of America, Monaca,     Pennsylvania     8 = EpiRez ® CMD W 603510 epoxy resin is an aqueous solution of 65     percent by weight supplied by Shell Chemical Co., Houston, Texas

Metal plate specimens were coated with the compositions of Examples 7and 8 and then air dried by the procedure described earlier. Thespecimens were then exposure tested for 1400 hours to determine theeffect of the corrosion inhibiting pigment in the composition on thecorrosion protection resulting therefrom. The test results are shownbelow in Table 9.

                  TABLE 9    ______________________________________    Blister Ratings    Test           Example 7                            Example 8    ______________________________________    Salt Spray     5        5    Humidity       75       0    ______________________________________

From the results provided in Table 9; if is seen that addition ofcorrosion inhibiting pigment in the polymeric component of Example 8reduces blister formation.

What is claimed is:
 1. A method of producing a corrosion-resistantcoating on a metal substrate comprising:mixing a stabilizing amount ofan amine-functional curing agent having at least two primary orsecondary amino groups with polymer particles of a latex polymer havinga Tg in the range of -50° C. to +50° C. to form an aqueous dispersion ofa polymeric component; mixing a corrosion protector component comprisinga corrosion resisting mount of a zinc dust with said polymeric componentwhereby said aqueous dispersion of said polymer particles is stabilizedin the presence of said corrosion protector component by saidmine-functional curing agent; mixing a crosslinking componentcoreactable with said amine-functional curing agent with said mixture ofsaid polymeric and said corrosion protector components to a form a potmix; applying a layer of said pot mix on said metal substrate; andcrosslinking said amine-functional curing agent with said crosslinkingcomponent in said layer to form said corrosion-resistant coating on saidmetal substrate.